An observation device is a shape measuring device for computing the surface height of a measurement object observed by a microscope, for example, to find its surface shape (for example, see Patent Literature 1). As shown, for example, in FIG. 14, in such a shape measuring device 500, a piezoelectrically driven device 530 continuously scans an objective 540 back and forth vertically (over a predetermined vertical range)—that is, along the optical axis of the microscope—at a rate of, for example, 15 times per second. During this back-and-forth scanning, images of a specimen 550 imaged by the objective 540 are captured by a high speed camera 51 at a ratio of one image per 1/900 second, converted to a digital signal, and outputted to a control processor 590. The control processor 590 calculates the degree of focusing (the extent of focusing) of each pixel of the inputted image, and finds the position in the optical axis direction in which the maximum degree of focusing has been detected for each pixel within a range from the upper-limit position to the lower-limit position of back-and-forth scanning as the relative height of the point corresponding to that pixel.